The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, in most of cameras, reflection type photometry devices are employed. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of the photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the determined brightness is greater than the actual brightness. If the camera controls an exposure operation based on thus determined exposure value, the object is under exposed. A dark object whose reflectivity is less than 18% is measured to have a lower brightness. Therefore, such an object is over exposed. The difference of the reflectivity of the object may also occur depending on the color of the object. For example, when the color of an object is yellow, the reflectivity may be up to 70%. In such a case, if the standard reflectivity is assumed to be 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 9%. In greater than necessary.
Therefore, in the conventional photometry device, the photographer is required to guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved. However, to accurately guess the reflectivity of the object and control the exposure can be done only by experienced and skilled photographers. It is impossible to require all the photographers to do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, cameras become unsuitable for recent trend of the automatic photographing.
It may be possible to measure the color of the object, and perform exposure compensation based on the reflectivity corresponding to the measured color. If such a control is performed, an appropriate exposure value seems to be obtained automatically regardless of the color of the object. To perform such operation, a plurality of sensors for colorimetry may be provided inside the camera for selectively measuring different portions of the object, and a so-called TTL colorimetry may be performed. That is, light passed through a photographing lens of the camera is received by the plurality of sensors. When such a structure is adopted, however, the spectral reflection characteristics of the object and the spectral radiant characteristic of an external light source are overlapped when the colorimetry is performed. Therefore, due to the spectral radiant characteristics of the external light source illuminating the object, it becomes difficult to measure the object color accurately. Then, the compensation amount of the exposure value includes errors, and the appropriate exposure may not be achieved.
It is therefore an object of the invention to provide an improved photometry device with which appropriate exposure values can be obtained regardless of difference of reflectivity of the objects without being affected by the spectral radiant characteristics of a light source illuminating the object.
For the above object, according to an aspect of the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor having spectral sensitivity characteristics close to visual sensitivity characteristics, a plurality of colorimetric sensors having spectral sensitivity characteristics that are different from those of the normal light sensor, an exposure amount determining system that determines an exposure amount of an object in accordance with an output of the normal light sensor, a colorimetry system that judges a color of the object in accordance with the outputs of the plurality of colorimetric sensors, an external light sensor that measures an external light illuminating the object at spectral sensitivity characteristics corresponding to each of the plurality of colorimetric sensors, the colorimetry system judging the color of the object by compensating the outputs of the plurality of colorimetric sensors based on the outputs of the external light sensor, a compensation amount determining system that determines an exposure compensation amount in accordance with the color judged by the colorimetry system, and a controller that compensates for the exposure amount determined by the exposure amount determining system in accordance with the exposure compensation amount.
With this configuration, since the exposure amount, which is determined similarly to a procedure in the conventional art is compensated in accordance with the color of the object. It should be noted that the color of the object is determined taking the characteristics of the light illuminating the object. Therefore, regardless of the color of the object, an appropriate exposure value can be obtained without being affected by the color of the light illuminating the object.
Optionally, the normal light sensor and the plurality of colorimetric sensors may receive light which is reflected by the object and passed through a photographing optical system, which includes a photographing lens, of the camera, and the external light sensor may receive light which is not passed through the photographing optical system of the camera.
Preferably, the normal light sensor may include a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, the plurality of colorimetric sensors may include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component, and the external light sensor may include a photometry sensor having photometry areas for metering blue, green and red light components, respectively.
Further preferably, the plurality of colorimetric sensors and the normal light sensor may include photometric elements having the same photometric characteristics. The external light sensor may also have the same photometric characteristics.
In this case, the blue light photometry sensor may be provided with a blue filter, the green light photometry sensor may be provided with a green filter, the red light photometry sensor may be provided with a red filter. Further, the external light sensor may be provide with filters, whose spectral transmissivity characteristics are substantially the same as those of the blue, green and red filters provided to the colorimetric sensors, at the plurality of photometry areas, respectively. In other words, the blue light photometry sensor, the green light photometry sensor, the red light photometry sensor and the photometry areas of the external light sensor have substantially the same spectral sensitivity characteristics, respectively.
Preferably, the normal light sensor, the plurality of colorimetric sensors and the external light sensor have substantially the same structure except the filters.
In particular, at the upper central portion of a pentagonal prism of the camera, the normal light sensor and the green light sensor are arranged side by side, the blue light sensor and the red light sensor are arranged on the eyepiece optical system side of the pentagonal prism, at right-and-left portions with respect to the eyepiece optical system, and the external light sensor may be arranged on an upper front position of the pentagonal prism, the external light sensor facing a window formed on a body of the camera so that the external light is incident on the external light sensor through said window.
In a particular case, the green light sensor may double as the normal light sensor.
Still optionally, the colorimetry system compensates for outputs of two of the colorimetry sensors in accordance with the outputs of the photometry areas of the external light sensor.
Further optionally, the colorimetry system may Judge at least yellow, blue and red from among yellow, magenta, cyan, blue, green and red, in accordance with the outputs of the plurality of colorimetry sensors. Then, the compensation amount determining system determines the exposure compensation amount in an over exposure side if the colorimetry system judges the color is yellow, and the compensation amount determining system determines the exposure compensation amount in an under exposure side if the colorimetry system judges the color is blue or red.
In this case, the compensation amount determining system may determine that the compensation amount is zero if the colorimetry system judges the color is magenta, cyan or green.
Still optionally, each of the normal light sensor, and the plurality of colorimetry sensors has divided photometry areas, and the exposure amount determining system and compensation amount determining system may determine the exposure amount and the exposure compensation amount in accordance with the outputs of each of the divided photometry areas.
In this case, the colorimetry system may judge the color of the object at each of the divided photometry areas, and the compensation amount determining system determines the exposure compensation amount for each of the divided photometry areas.
Then, the exposure amount determining system may determine an exposure compensation amount for the entire object by applying a predetermined calculation to the exposure compensation amounts obtained for the plurality of divided photometry areas.